1. Field of the Invention
The present invention relates generally to an industrial gas turbine engine, and more specifically to a turbine exhaust cylinder cooling of an industrial gas turbine engine.
2. Description of the Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
In a gas turbine engine, such as a large frame heavy duty industrial gas turbine engine used to produce electric power, a hot gas stream is passed through a multiple stage turbine to drive a compressor and an electric generator. The turbine exhaust is channeled through a turbine exhaust casing to safely discharge the hot exhaust gas out from the engine and surrounding environment. The turbine exhaust gas is still rather hot and can erode parts of the engine downstream from the turbine. The turbine exhaust casing is supported by a number of struts that pass through fairings that have an airfoil shape. FIG. 1 shows a prior art engine with a turbine exhaust casing in which a strut 14 passing through a fairing 18. The last stage turbine rotor blade 11 rotates along with a rotor disk 12. An engine casing 13 supports the struts 14 and fairings 18. A cover plate 15 enclosed the space. A tie rod 16 connects the casing 13 to an outer diameter cylinder 27. An inner diameter cylinder 19 is located inward of the OD cylinder 27 and together forms a flow path for the turbine exhaust. A man-way 20 is formed between an exhaust cylinder 21 and an enclosure 22. The engine center line is labeled C.L. in FIG. 1. In this embodiment, no cooling is provided for the fairing 18 and struts 14
FIG. 2 shows a front view of the turbine exhaust casing support with the casing 13 supporting six struts 14 that each pass through a separate fairing 18. The inner ends of the struts 14 are secured to a bearing housing 24. The turbine exhaust gas flow path is formed between the inner diameter cylinder 19 and the outer diameter cylinder 27 and flows around the fairing 18.
FIG. 3 shows an embodiment in which the struts 14 and the fairings 18 are cooled by passing ambient air through the fairings 18. Ambient cooling air is drawn into the exhaust casing through the cover plate 15 and then flows through the space formed between the struts 14 and the fairings 18. There are six cover plates 15 open with one cover plate 15 for each of the struts 14 and fairings 18. During engine operation, the flow path pressure ID of the blade exhaust cylinder junction is lower than the ambient pressure. Cooling air is sucked in due to this pressure differential. At a 100% loading condition, the maximum delta pressure is around 1.0 psi. Such low pressure differential is not enough to induce a large amount of ambient cooling air into the exhaust cylinder to provide adequate cooling for the struts and casing. At some operational point, the delta pressure is even lower than 1.0 psi. As a result of inadequate available cooling, high temperature resistant materials are used for the struts and the casing in the design and therefore significantly increase the design cost.